Polar Kinematics

If we have a position vector [tex] \vec{r} = x\vec{i} + y\vec{j} [/tex] why is the polar form of the equation [tex] r = r\vec{r} [/tex]? Don't we need two parameters to define a postition? And [tex] r [/tex] is the magnitude of [tex] \vec{r} [/tex]?

If we have a position vector [tex] \vec{r} = x\vec{i} + y\vec{j} [/tex] why is the polar form of the equation [tex] r = r\vec{r} [/tex]? Don't we need two parameters to define a postition? And [tex] r [/tex] is the magnitude of [tex] \vec{r} [/tex]?